CVE-2017-1000101 in macOS
Summary
by MITRE
curl supports "globbing" of URLs, in which a user can pass a numerical range to have the tool iterate over those numbers to do a sequence of transfers. In the globbing function that parses the numerical range, there was an omission that made curl read a byte beyond the end of the URL if given a carefully crafted, or just wrongly written, URL. The URL is stored in a heap based buffer, so it could then be made to wrongly read something else instead of crashing. An example of a URL that triggers the flaw would be `http://ur%20[0-60000000000000000000`.
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Analysis
by VulDB Data Team • 01/21/2021
The vulnerability identified as CVE-2017-1000101 resides within the curl command-line tool and represents a classic buffer overread condition that can potentially lead to information disclosure or arbitrary code execution. This flaw specifically impacts curl's URL globbing functionality, which allows users to specify numerical ranges in URLs to perform multiple transfers sequentially. The vulnerability manifests when curl processes URLs containing malformed glob patterns, particularly those with extremely large numerical ranges that exceed the bounds of the allocated memory buffer. The issue stems from inadequate bounds checking within the globbing parsing function that handles numerical range specifications, creating a scenario where the application reads memory beyond the intended buffer boundaries.
The technical implementation of this vulnerability involves curl's heap-based memory management system where URL strings are stored in dynamically allocated buffers. When processing a malformed URL such as `http://ur%20[0-60000000000000000000]`, the globbing parser fails to properly validate the numerical range parameters, causing it to traverse beyond the allocated buffer space. This overread condition occurs because the parsing logic does not adequately check the boundaries of the numerical range specification against the actual buffer size, allowing the application to access adjacent memory locations that may contain sensitive data or other program state information. The vulnerability is particularly concerning because it operates within the heap memory space, making it more difficult to predict and exploit compared to stack-based buffer overflows, and potentially allowing attackers to extract information from other heap allocations.
The operational impact of this vulnerability extends beyond simple information disclosure, as it can potentially be leveraged for more sophisticated attacks depending on the system configuration and memory layout. An attacker who successfully exploits this overread condition could potentially extract sensitive information from adjacent heap memory regions, including credentials, session tokens, or other confidential data that might be stored in memory. The vulnerability's exploitation requires careful crafting of the URL pattern to trigger the specific overread condition, but once triggered, it can provide attackers with access to memory contents that could be used for further exploitation or reconnaissance. The large numerical range specified in the example demonstrates how seemingly benign input validation failures can create conditions for memory corruption that may not immediately manifest as crashes but instead provide data leakage opportunities.
Security mitigations for this vulnerability primarily focus on input validation and bounds checking within the curl application's globbing functionality. The most effective approach involves implementing proper parameter validation to ensure that numerical range specifications remain within reasonable bounds and do not exceed the allocated buffer capacity. System administrators should ensure that curl installations are updated to versions that contain the patched globbing implementation, which typically includes enhanced bounds checking and proper error handling for malformed URL patterns. Additionally, network security controls such as web application firewalls and URL filtering systems can help prevent malicious URLs from reaching curl applications by implementing strict validation rules for URL patterns and numerical range specifications. The vulnerability aligns with CWE-125, which describes out-of-bounds read conditions, and could potentially be categorized under ATT&CK technique T1059 for command and scripting interpreter usage, particularly when attackers leverage curl for malicious data exfiltration or reconnaissance activities. Organizations should also consider implementing monitoring solutions to detect unusual curl usage patterns that might indicate exploitation attempts, as the vulnerability's impact is most pronounced when curl is used in automated or scripted environments where attackers can systematically test for memory leakage conditions.